Mucopolysaccharidosis I, or MPSI, is a spectrum of disorders caused by a lysosomal storage disorder. This deficiency of an enzyme in the lysosome or digestive organ of the cell leads to an accumulation of large amounts of the substrates called mucopolysaccharides. This accumulated material causes severe multisystem disease in these patients, including mental retardation, heart disease, respiratory disease, joint stiffness, bone deformity and often leads to death. This study will evaluate the safety and efficacy of enzyme replacement therapy in the treatment of MPS I. Safety and effects of the enzyme on lysosomal storage in the liver, spleen, urine and other sites as well will be evaluated.